Step 1: Prepare the Chicken

1. Season and Coat with Cornstarch: Season the chicken pieces with a pinch of salt and black pepper. Sprinkle 1 tablespoon of cornstarch over the chicken and toss to coat. This helps create a light crust on the chicken and allows the sauce to adhere better.
2. Marinate (Optional): If you have a few extra minutes, let the chicken sit with the cornstarch for 10 minutes. This helps to tenderize the meat and ensures a juicy texture.

Step 2: Make the Sauce

1. Combine Sauce Ingredients: In a small bowl, whisk together the soy sauce, oyster sauce, rice vinegar, sugar, sesame oil, and cornstarch. Add the chicken broth, minced ginger, and minced garlic, stirring until smooth. This sauce will bring the dish together with a rich and flavorful glaze.

Step 3: Cook the Chicken

1. Heat Oil in Pan: In a large skillet or wok, heat 1 tablespoon of vegetable oil over medium-high heat.
2. Cook Chicken: Add the chicken pieces to the skillet in a single layer. Let them cook without stirring for 2-3 minutes, allowing them to get a golden crust on one side. Flip and cook for an additional 2-3 minutes, until the chicken is cooked through. Remove the chicken from the pan and set it aside.

Step 4: Stir-Fry the Vegetables

1. Add More Oil if Needed: If the pan seems dry, add a bit more oil before adding the vegetables.
2. Stir-Fry Mushrooms: Add the sliced mushrooms to the skillet and cook for 2-3 minutes, or until they are tender and slightly browned.
3. Add Zucchini: Add the zucchini to the skillet and cook for another 2 minutes, or until they are just tender but still crisp. You want the zucchini to retain some crunch to provide contrast to the dish.

Step 5: Combine Chicken, Vegetables, and Sauce

1. Return Chicken to Pan: Add the cooked chicken back to the skillet with the mushrooms and zucchini.
2. Pour in the Sauce: Pour the sauce mixture over the chicken and vegetables. Stir everything together to coat evenly.
3. Cook Until Thickened: Continue to cook for another 2-3 minutes, or until the sauce has thickened and everything is well coated. The cornstarch in the sauce will help it cling to the chicken and vegetables.

Step 6: Serve and Garnish

1. Garnish: Transfer the Mushroom Chicken to a serving bowl. Sprinkle with sesame seeds and sliced green onions for added flavor and presentation.
2. Serve with Rice: Serve over steamed rice or noodles for a complete meal.